Effect of boric oxide doping on the stability and activity of a Cu–SiO2 catalyst for vapor-phase hydrogenation of dimethyl oxalate to ethylene glycol

Stable and efficient B–Cu–SiO2 catalysts for the hydrogenation of dimethyl oxalate (DMO) to ethylene glycol were prepared through urea-assisted gelation followed by postimpregnation with boric acid. Auger electron spectroscopy and CO adsorption by in situ Fourier transform infrared spectroscopy revealed that the Cu+ species on the catalyst surface increased together with an increase in the amount of boric oxide dopant. X-ray diffraction and N2O chemisorption indicated that a suitable amount of boric oxide doping tended to improve copper dispersion and retard the growth of copper particles during DMO hydrogenation. Catalytic stability was greatly enhanced in the B–Cu–SiO2 catalyst with an optimized Cu/B atomic ratio of 6.6, because of the formation and preservation of appropriate distributions of Cu+ and Cu0 species on the catalyst surfaces. The effect of boric oxide was attributed to its relatively high affinity for electrons, which tended to lower the reducibility of the Cu+ species.